The feasibility study of Mai Hydropower Project (MHP) was undertaken by Sanima Hydropower (P.) Ltd. Initially, in June 2006, MHP was proposed as a daily peaking run of river project with installed capacity of 20.1 MW. After discussion with Nepal Electricity Authority(NEA), the daily peaking option was abandoned (as recommended by NEA, the government’s power utility to purchase power from the Project) and an optimum simple run-of river scheme with installed capacity of 14.5 MW was technically concluded with NEA in year 2007 with the energy price open for negotiation.
In year 2008, Sanima Hydropower (P.) Limited (SHPL) established a Special Purpose Vehicle Company “Sanima Mai Hydropower (P.) Limited (SMHPL)” for the implementation of Mai Hydropower Project. After incorporation of SMHPL, Sanima Hydropower (P.) Limited applied to Department of Electricity Development (DoED) for transfer of license into SMHPL which in turn obtained the license in March 2009 from the Department.
In year 2009, NEA declared new power purchase tariff for projects below 25 MW being developed by national private power producers. The declaration of new rate has limited the developer for negotiation in electricity tariff. However there are some issues regarding the VAT and income tax as well as the definition of dry and wet season for which the government of Nepal is preparing to address through new hydropower regulation.
At present, the company has purchased private land required by the Project and track opening of shortest access road between powerhouse and headworks have been completed. However the headworks and powerhouse site are connected with existing motorable road networks. The process of obtaining permission for tree cutting and government land on lease has been completed and awaited for its approval.
There has been some major changes to the feasibility study design in the arrangement of headworks. Other changes are relocation of powerhouse building after the geotechnical investigation (core-drilling). The changes have enhanced the project both technically and financially. The revised capacity of the Project is 15.6 MW.
The Mai Hydropower Project is defined as 15.6 MW (2×7.8 MW) installed capacity with design discharge of 16 m3/s and net head of 112.71 m. The project site is located at a distance of 30 km north from Birtamod in East-West Highway. Headworks of the project is located on the Mai Khola between the boarder of two Village Development Committees (VDCs) namely Chisapani and Soyak in Ilam District. Right bank of the diversion dam lies in Soyak VDC of Ilam district. The powerhouse site is located at Musekhop village approximately 4.5 km upstream from the confluence of the Lodhiya Khola and Mai Khola in Danabari VDC of Ilam district. Both the powerhouse and headworks are accessible by existing motorable road.
The headworks comprises the concrete gravity dam of 10.6 m height from the deepest foundation level. The crest length of the dam is 85.92 m and the crest elevation is fixed at 320.6 m amsl. The intake of water is made through the combined arrangement of undersluice, power-intake and trash-remover provisioned for floating debris. Three undersluices of size 6.0 m wide by 2.0 m height are placed with hydraulic radial gates. The arrangement of the intake is as shown in drawing MHP-12-T01 to T03.
Total length of 80m long pressurized section (approach canal) conveys water into the settling basin. Four chambered settling basin with parallel section width of 6.5 m center to center and length 75.0 m has been proposed. The depth of the basin is 5.5 m at the start of the parallel section and 6.25 m at the end. The top level of the settling basin side walls is fixed at 321.0m amsl and the water level in the settling basin is 320.0 m amsl.
Settling basin is proposed as a conventional gravity flushing. From the end of the settling basin, the water is conveyed through the pressurized culvert of 1072.0m length with 3.5 m width by 3.3 m clear height inside. The culvert ends at the inlet tunnel portal. The arrangement of tunnel inlet portal is shown in drawing MHP-18-T01.
The length of the headrace tunnel is 2192 m and the section is inverted D-shaped with cross-sectional area of 13.1 m2-finish and 11.37 m2-finish for 66 m long inverted D-shaped tunnel after the surge tank. The tunnel is proposed with concrete lining in the invert (whole length) and appropriate rock-support for the rest as shown in the drawing MHP-18-T02. Surge-shaft is located at 2126 m length along the tunnel measured from the inlet portal and is exposed to the surface. The height of the surge-shaft is 27 m (Top elevation at 332.2 m amsl, and bottom at tunnel invert is 300.0 m amsl. The finish diameter of the surge-shaft is 8.0 m.
The change to the feasibility study is the location of powerhouse which has now been shifted towards waterway side reducing the length of the penstock by about 100m. The penstock length starting from tunnel outlet up to the Wyee-furcation is 273.6 m and the diameter is 2350 mm. The penstock branches into two feeder pipes of diameter 1500 mm each and the length of each branch is 40.4 m upto the butterfly valve supplied by the equipment supplier. The Penstock and anchor/thrust block arrangement is as shown in drawings MHP-20-T01,T02.
The Powerhouse is semi-surface type with turbine floor below the ground elevation. The size of the powerhouse is 27.3 m x 22 m. The minimum elevation of the foundation at the draft tube is 195.85m amsl and the elevation of the crane-beam is 210.98 m amsl. The elevation of the tubine floor and governor floors are 200.87 m amsl and 205.0 m amsl respectively and the total clear height of the powerhouse from governor floor is 13.31 m. 200 m long tailrace RCC canal conveys water from powerhouse and discharges into the Canal Intake of the Mai Cascade Project (to be constructed and operated in tandom with the Mai Hydropower Project with a lag of 6 months).
The generated power is evacuated through the 132 kV transmission line of 12.6 km length. The transmission line connects to the national grid through the proposed Ilam Hub.
MHP posseses characteristics very desirable for the INPS system by serving to reduce technical loss, improve the voltage profile and power supply scenario in the region. In addition, this Project will help to reduce the operation of the expensive thermal power to some extent and dependency on Indian system for the Eastern Nepal. The Project’s proximity to the power-hungry Eastern load center of Nepal will be the biggest attraction of NEA. Further the realization of MHP will help industrialization of the power hungry eastern Terai belt of Nepal and similarly many Nepali skilled, semiskilled and unskilled workers will have an opportunity to get employment during construction and to some extent post construction period that strengthens the local economy. The environmental and social impacts are moderate to low typical for the run-of-river project.
The project cost on the basis of unit rates as applicable on May 2009 is NPR 2658 million. The construction period of 42 months (3.5 years) has been estimated including testing and commissioning. The gross energy production is 105.383 GWh and the net annual energy is 102.462 GWh of which about 21.3% (21.861 GWh) is dry season (Poush to Chaitra) energy and the rest 80.601 GWh is the wet season energy.
The financial parameters of the Project are moderate to low at the recently declared energy rates which are at the lower side that could hardly add significant megawatts to the Integrated Nepal Power System. This Project and the projects on pipeline desperately awaiting the government’s new policies to be declared. This Project Company to implement the Mai Hydropower Project assumes the followings points that will appear (as has been prepared by the government and discussed among the stakeholders too) as:
a. VAT on civil construction be exempted, and goods to be imported for the construction shall be applicable for 1% duty only and not the VAT,
b. Dry season of 6 months shall be declared for the purpose of fixing the dry and wet season energy and their corresponding energy rates,
c. Income tax for first 10 years be exempted, then for the rest of the period imposed fully,
d. Government shall provide working environment at the project sites in terms of securities (all political parties shall have strong commitment and common views and welcoming attitudes on these development activities including their caders at the local level).